half-earth/materials/cursor.tres

@@ -0,0 +1,9 @@
+[gd_resource type="ShaderMaterial" load_steps=2 format=2]
+
+[ext_resource path="res://shaders/tile_shader.gdshader" type="Shader" id=1]
+
+[resource]
+shader = ExtResource( 1 )
+shader_param/baseColor = Color( 0.992157, 1, 0, 1 )
+shader_param/highlightColor = Color( 1, 0, 0.984314, 1 )
+shader_param/isHighlighted = 0

half-earth/materials/tile.tres

@@ -5,4 +5,6 @@
 [resource]
 resource_local_to_scene = true
 shader = ExtResource( 1 )
-shader_param/c = null
+shader_param/baseColor = Color( 0.0823529, 0, 1, 1 )
+shader_param/highlightColor = Color( 1, 0, 0, 1 )
+shader_param/isHighlighted = null

half-earth/nodes/grid_cursor.tscn

@@ -0,0 +1,10 @@
+[gd_scene load_steps=4 format=2]
+
+[ext_resource path="res://textures/icon.png" type="Texture" id=1]
+[ext_resource path="res://scripts/GridCursor.cs" type="Script" id=2]
+[ext_resource path="res://materials/cursor.tres" type="Material" id=3]
+
+[node name="Grid Cursor" type="Sprite"]
+material = ExtResource( 3 )
+texture = ExtResource( 1 )
+script = ExtResource( 2 )

half-earth/scripts/GridCursor.cs

@@ -0,0 +1,51 @@
+using Godot;
+using System;
+
+public class GridCursor : Sprite
+{
+    [Export]
+    public NodePath Grid { get; set; }
+    private WorldGrid _grid;
+    private ShaderMaterial _material;
+
+    private const string IS_HIGHLIGHTED = "isHighlighted";
+
+    public override void _Ready()
+    {
+        _grid = GetNode<WorldGrid>(Grid);
+        _material = (ShaderMaterial)Material;
+    }
+    
+    public override void _Input(InputEvent @event)
+    {
+        base._Input(@event);
+        
+        if (@event is InputEventMouseMotion mouseMoveEvent)
+        {
+            var pos = mouseMoveEvent.Position;
+            _grid.GetGridPos(pos, out var x, out var y);
+            this.Visible = _grid.IsInBounds(x, y);
+            var position = new Vector2(x + .5f, y + .5f) * _grid.CellSize;
+            this.Position = position;
+        }
+        else if (@event is InputEventMouseButton mouseButtonEvent)
+        {
+            switch ((ButtonList)mouseButtonEvent.ButtonIndex)
+            {
+                case ButtonList.Left:
+                    if (mouseButtonEvent.Pressed)
+                    {
+                        var pos = mouseButtonEvent.Position;
+                        _grid.GetGridPos(pos, out var x, out var y);
+                        _grid.ToggleTileHighlight(x, y);
+                        _material.SetShaderParam(IS_HIGHLIGHTED, 1);
+                    }
+                    else
+                    {
+                        _material.SetShaderParam(IS_HIGHLIGHTED, 0);
+                    }
+                    break;
+            }
+        }
+    }
+}

half-earth/scripts/WorldGrid.cs

@@ -14,7 +14,7 @@ public class WorldGrid : Node2D
     
     private struct Tile
     {
-        public float data;
+        public bool isHighlighted;
         public ShaderMaterial material;
     }
     private Tile[,] _tiles;
@@ -35,18 +35,25 @@ public class WorldGrid : Node2D
             {
                 var tile = _tiles[x, y];
                 var material = tile.material;
-                material.SetShaderParam("c", tile.data);
+                material.SetShaderParam("isHighlighted", tile.isHighlighted ? 1 : 0);
             }
         }
     }
     
+    public bool IsInBounds(int x, int y)
+    {
+        return x >= 0 && x < Size && y >= 0 && y < Size;
+    }
+
+    public void ToggleTileHighlight(int x, int y)
+    {
+        _tiles[x, y].isHighlighted ^= true;
+    }
+
     public void GetGridPos(Vector2 position, out int x, out int y)
     {
-        int GetCoord(float f) =>
-            Mathf.Clamp(Mathf.FloorToInt(f / CellSize), 0, CellSize -1);
-
-        x = GetCoord(position.x);
-        y = GetCoord(position.y);
+        x = Mathf.FloorToInt(position.x / CellSize);
+        y = Mathf.FloorToInt(position.y / CellSize);
     }
 
     private void Clear()
@@ -73,7 +80,7 @@ public class WorldGrid : Node2D
             for (int y = 0; y < size; y++)
             {
                 var tile = new Tile();
-                tile.data = (float)(y * size + x) / 100f;
+                tile.isHighlighted = false;
                 
                 var node = TileScene.Instance<Node2D>();
                 this.AddChild(node);

half-earth/shaders/tile_shader.gdshader

@@ -1,7 +1,9 @@
 shader_type canvas_item;
 
-uniform float c;
+uniform vec4 baseColor : hint_color;
+uniform vec4 highlightColor : hint_color;
+uniform int isHighlighted;
 
 void fragment() {
-	COLOR = vec4(c, 0.0, 0.0, 1.0);
+	COLOR = mix(baseColor, highlightColor, float(isHighlighted));
 }